A flexible container can be used to contain a liquid. The container includes flexible panels of plastic sheet material that are adjoined together along their edges to form a pouch with a top opening. A rigid fitment is sealed into the pouch's top opening. A channel in the fitment provides access to the interior of the pouch for filling and emptying the pouch. The fitment has an external screw thread by which a bottle cap is screwed onto the fitment to seal off the container.